BUB3 (BUB3 mitotic checkpoint protein)

2019-03-01   Jorge Antonio Elias Godoy Carlos , Joao Agostinho Machado-Neto 

Department of Pharmacology, Institute of Biomedical Sciences of the University of São Paulo, São Paulo, Brazil; jorgegdy@icloud.com; jamachadoneto@usp.br




BUB3 is a WD40 protein that belongs to spindle mitotic checkpoint complex, which monitors the chromosome attachment to mitotic (or meiotic) fuse and prevents premature chromosome segregation. Alterations in BUB3 have been associated with chromosomal instability and aneuploidy, but their contribution for cancer development and progression are poorly understood, and appear to differ depending on the type of cancer. The present review contains data on BUB3 DNA, RNA, protein encoded and function.



The entire BUB3 gene is approximately 16.2 Kb (start: 123154277 and end: 123170467 bp; orientation: Forward strand).


The BUB3 gene encodes for 4 transcript variants: there are two transcript variants deposited in the NCBI database (https://www.ncbi.nlm.nih.gov/gene) and two additional transcript variants reported in Ensembl (http://www.ensembl.org/). The transcript variant 1 is the longest transcript variant (exons: 8, coding exons: 7, transcript length: 7828 bp) and encodes the isoform a (328 amino acids [aa]). The transcript variant 2 present an alternative splice site in 3 coding region (exons: 8, coding exons: 7, transcript length: 1361 bp), which leads to a frameshift and a shorter and distinct C-terminus compared to isoform a (isoform b, 326 aa). The transcript variant 3 present 6 coding exons, a transcript length of 895 bp and a translation length of 278 aa. The transcript variant 4 is shorter transcript presenting 5 exons (being 4 coding exons), a transcript length 667 bp and resulting protein of 145 aa.


Atlas Image
Figure 1. BUB3 protein structure. BUB3 protein presents seven WD40 repeat domain, a nearly 40 amino acids (aa) motif rich in tryptophan-aspartic acids (W-D). The position of aa are indicated.


BUB3 is a WD40 protein that create a symmetric circular wall around a central pore or funnel region with its seven-blade β-propeller structure, acting as a scaffolding protein for its binding partners BUB1B (BUBR1) and BUB1 (Prinz et al., 2016; Seeley et al., 1999). The primary structure of BUB3 is illustrated in Figure 1.




BUB3 is localized preferentially in unattached kinetochores during mitosis (especially prometaphase), participating of mitotic checkpoint complex (Sudakin et al., 2001). In interphase cells, BUB3 is localized in cytosol (Yoon et al., 2004).
Atlas Image
Figure 2. BUB3, a component of mitotic checkpoint complex (MCC). (Upper panel) The presence of unattached kinotochores induces the formation of MCC composed by BUB3, BUBR1, MAD2L1, which sequester CDC20, leads the anaphase-promoting complex/cyclosome (APC/C) inhibition and cell cycle arrest. (Lower panel) In the presence of attached kinotochores, the MCC complex is disassembled and the CDC20 is released, which leads to APC/C activation (which in turn triggers degradation of securin and cyclin B), chromosomal segregation and completion of mitosis.


BUB3 protein is a component of the mitotic checkpoint complex (MCC), which present a crucial activity monitoring the state of chromosome attachment to the mitotic (or meiotic) fuse and prevents loss of sister chromatid cohesion and premature chromosome segregation in the presence of unattached or incorrectly attached chromosomes to the spindle by inhibition of the anaphase-promoting complex/cyclosome (APC/C) (Lopes et al., 2005; Musacchio, 2015). The canonical BUB3-related cellular signaling is illustrated in Figure 2.
Using a Drosophila melanogaster model, Morais da Silva and colleagues (Morais da Silva et al., 2013) reported that BUB3 inhibition resulted in increased proliferative potential, promoted tumorigenesis and widespread chromosomal aneuploidy. Interesting, loss of cytoplasmatic, but not attached-kinetochore, BUB3 pool was found to be driven tumorigenesis, indicating a novel non-kinetochore-dependent tumor suppressing function for BUB3 (Morais da Silva et al., 2013). Additional non-canonical functions of BUB3 had been described during interphase. BUB3 and CDC20 form a complex with histone deacetylases, which seems to confer transcriptional repressor activity (Yoon et al., 2004). Wan and colleagues (Wan et al., 2015) reported that BUB3 regulates RNA splicing, R-loop formation, DNA damage, and TP53 activation.


The BUB3 gene and protein is highly homologous among different species, as shown in Table 1.
Table 1. Comparative identity of human BUB3 with other species.
% Identity for: Homo sapiens BUB3  SymbolProtein  DNA
vs. P.troglodytesBUB3100.099.8
vs. M.mulattaBUB3100.098.8
vs. B.taurusBUB3100.093.5
vs. M.musculusBub3100.090.4
vs. R.norvegicusBub3100.091.1
vs. G.gallusBUB396.984.0
vs. X.tropicalisbub393.279.5
vs. D.reriobub386.273.7
vs. D.melanogasterBub361.159.9
vs. A.gambiaeAgaP_AGAP01054462.059.2
vs. S.pombebub338.045.0
vs. A.thalianaBUB3.155.155.0
vs. A.thalianaBUB3.256.355.8
vs. O.sativaOs03g044860056.357.4

(Source: http://www.ncbi.nlm.nih.gov/homologene)



Recurrent mutations in the BUB3 gene are rare. A total of 81 unique samples presented BUB3 mutations, which are distributed on 75 different mutations (60 missense substitutions, 10 synonymous substitutions, 1 nonsense substitutions, 2 inframe deletions and 2 frameshift deletions), were found among the 47120 unique samples reported in COSMIC (Catalogue of Somatic Mutations in Cancer; http://cancer.sanger.ac.uk/cancergenome/projects/cosmic). In agreement, 0.2% of 74247 tested samples presented BUB3 somatic mutation as reported in cBioPortal (http://www.cbioportal.org), which correspond to 154 mutations: 132 missense substitutions, 17 truncating and 5 inframe mutations. Of note, there are 55 duplicate mutations in patients with multiple samples. A total of 472 (0.8 %) samples presented any type of genetic alteration in BUB3, when mutations, amplifications, deep deletions and multiple alterations were considered in 55817 cancer samples. These findings corroborate initial studies in different types of cancer (Hernando et al., 2001).

Implicated in

Entity name
Adrenocortical carcinoma
In a cohort of 79 adrenocortical carcinoma patients, increased levels of BUB3 mRNA levels was associated with high grade tumors and poor clinical outcomes (Subramanian and Cohen, 2019). In addition, Oncomine Giordano ACC data analysis revealed increased levels of BUB3 in adrenocortical carcinoma compared to normal adrenal samples (Subramanian and Cohen, 2019).
Entity name
Breast cancer
BUB3 promoter polymorphisms (rs3763740, rs3763741, rs17014712, rs3808960 and rs3808961) did not impact familial breast cancer risk in a German cohort of 441 breast cancer patients and 552 controls matched by age, ethnicity and geographical region (Vaclavicek et al., 2007). Similarly, the polymorphisms rs11248416, rs11248419, and rs6599657 in BUB3 gene were not associated with risk of breast cancer development in a Chinese cohort of 462 breast cancer patients and 529 controls (Wang et al., 2014).
BUB3 was highly expressed in primary and cell lines from breast cancer compared to immortalized breast cancer epithelium or normal primary mammary cells (Yuan et al., 2006). BUB3 gene region (10q26.3) was found to be amplified and overexpressed in breast cancer samples (Turner et al., 2010). BUB3 mRNA levels were upregulated in doxorubicin and cyclophosphamide sensitive breast cancer tumors (Cleator et al., 2006). In MDA-MB-231 breast cancer cells, BUB3 expression was induced by BMP signaling (Yan et al., 2012).
Entity name
Cervical cancer
Using proteomics approach, BUB3 was found to be downregulated by paclitaxel and 5-fluorouracil in HeLa cells (Lee et al., 2005; Yim et al., 2004). In addition, BUB3 inhibition by siRNA reduced paclitaxel-induced cell cycle arrest (Lee et al., 2005).
BCR/ ABL1 expression repressed spindle checkpoint components, including BUB3, to escape from metaphase arrest (Wolanin et al., 2010).
Entity name
Colorectal cancer
Three missense variants in BUB3 [predicted to be pathogenic: c.790T>C (p.F264L), c.63G>C (p.K21N) and c.446G>A (p.R149Q)] were observed in familial or early onset colorectal cancer patients (n=185), which were not found in large cohort of control (n=1154) (de Voer et al., 2013). In agreement, Mur and colleagues (Mur et al., 2018) reported that BUB3 was found to be mutated [BUB3 c.77C>T (p.T26I)] in familial colorectal cancer.
Entity name
Gastric cancer
High BUB3 gene expression was observed in 34 out of 43 gastric cancer tumors samples compared with their matched normal mucosa counterpart, which was associated with Ki-67 expression, but not with aneuploidy (Grabsch et al., 2003). The BUB3 polymorphism, rs7897156, did not impact gastric cancer susceptibility in a study including 164 gastric cancer patients and 381 ethnicity matched controls (Mesic et al., 2017).
Entity name
he genetic variation C>T in the position -6 of the BUB3 gene, but not in coding sequence, was detected in 4 out of 22 glioblastoma samples (Reis et al., 2001). Bie and colleagues (Bie et al., 2011) reported that BUB3 was highly expressed in grade III and IV gliomas compared to normal brain samples. On the other hand, Morales and colleagues (Morales et al., 2013) reported a downregulation of BUB3 in primary samples and cell lines derived from glioblastoma compared to non-neoplastic white matter from epileptic patients.
In BUB3-depleted U87MG glioblastoma cells, the expression o BUB3Y207F, which mimics an unphosphorylated form, strongly reduced tumor growth and improved survival compared to the expression BUB3WT in intracranial tumor mice model, indicating that BUB3 phosphorylation at Y207 site is required for tumorigenesis (Jiang et al., 2014).
Entity name
Lung cancer
Initial observations did not identify genetic defects in BUB3 gene in lung cancer patients (Haruki et al., 2001). In cohort of 766 non-small cell lung cancer patients, the presence of allele T of polymorphism in BUB3 (rs7897156C>T) was associated with poor overall survival (Kang et al., 2017). Using H1299 and A549 non-small cell lung cell lines, functional studies based in luciferase assays indicated that T allele induced enhancement of BUB3 expression. In addition, increased BUB3 expression was observed in lung tumor tissues compared to non-malignant lung tissues (Kang et al., 2017).
Entity name
Loss of heterozygosity at 10q26, but not BUB3 mutations, was found in ostesarcoma samples (Mendoza et al., 2005). In Saos-2 osteosarcoma cells, TAp73α (an isoform of TP73) binds to BUB3 and BUB1, which leads to potential alteration of mitotic checkpoint function of these proteins and aneuploidy (Vernole et al., 2009). In U2OS osteosarcoma cells, but not normal fibroblast, BUB3 silencing reduces cell proliferation and clonogenicity and induces DNA fragmentation (Prinz et al., 2016).
Entity name
Ovarian cystadenoma
In ML10 cells, a human ovarian cystadenoma model, BUB3 nuclear expression and phosphorylation were increased in low compared to high replicative age cells, which may be involved in prolonged mitotic arrest and cytokinesis failure observed in this cellular model (Austria et al., 2018).
Entity name
Pancreatic cancer
A mutation in BUB3 (c.576+1G>A) was found among deleterious germline mutations (n=33) in sporadic pancreatic adenocarcinoma patients (n=854) (Shindo et al., 2017). In pancreatic cells, DMAP1/BUB3 complex repressed antiapoptotic genes transcription mediating mitotic stress-induced apoptosis and improved in vivo paclitaxel-induced tumor growth inhibition, which are impaired by SRC activity (Li et al., 2018).
Entity name
Renal cell carcinoma
BUB3 gene expression profile was similar between samples from papillary renal cell carcinoma, chromophobe renal cell carcinoma and clear cell renal cell carcinoma patients and normal kidney tissues (Pinto et al., 2007; Pinto et al., 2008).


Pubmed IDLast YearTitleAuthors
299789152018Mechanism of cytokinesis failure in ovarian cystadenomas with defective BRCA1 and P53 pathways.Austria T et al
125519522003Rae1 is an essential mitotic checkpoint regulator that cooperates with Bub3 to prevent chromosome missegregation.Babu JR et al
220224242011The accuracy of survival time prediction for patients with glioma is improved by measuring mitotic spindle checkpoint gene expression.Bie L et al
163228992006Gene expression patterns for doxorubicin (Adriamycin) and cyclophosphamide (cytoxan) (AC) response and resistance.Cleator S et al
274245242016Genetic variation in the major mitotic checkpoint genes associated with chromosomal aberrations in healthy humans.Försti A et al
126928362003Overexpression of the mitotic checkpoint genes BUB1, BUBR1, and BUB3 in gastric cancer--association with tumour cell proliferation.Grabsch H et al
111462262001Molecular analysis of the mitotic checkpoint genes BUB1, BUBR1 and BUB3 in human lung cancers.Haruki N et al
114001142001Molecular analyses of the mitotic checkpoint components hsMAD2, hBUB1 and hBUB3 in human cancer.Hernando E et al
243162232014PKM2 regulates chromosome segregation and mitosis progression of tumor cells.Jiang Y et al
158981112005Increased chromosome instability but not cancer predisposition in haploinsufficient Bub3 mice.Kalitsis P et al
289779032017Polymorphisms in mitotic checkpoint-related genes can influence survival outcomes of early-stage non-small cell lung cancer.Kang HG et al
159079832005Proteomic analysis of anti-cancer effects by paclitaxel treatment in cervical cancer cells.Lee KH et al
305532762018C-Src confers resistance to mitotic stress through inhibition DMAP1/Bub3 complex formation in pancreatic cancer.Li J et al
156157832005The Drosophila Bub3 protein is required for the mitotic checkpoint and for normal accumulation of cyclins during G2 and early stages of mitosis.Lopes CS et al
157969612005Allelic loss at 10q26 in osteosarcoma in the region of the BUB3 and FGFR2 genes.Mendoza S et al
288430042017Single nucleotide polymorphisms rs911160 in AURKA and rs2289590 in AURKB mitotic checkpoint genes contribute to gastric cancer susceptibility.Mesic A et al
294489352018Germline mutations in the spindle assembly checkpoint genes BUB1 and BUB3 are infrequent in familial colorectal cancer and polyposis.Mur P et al
264853652015The Molecular Biology of Spindle Assembly Checkpoint Signaling Dynamics.Musacchio A et al
112393972001Suppression of spontaneous chromosomal rearrangements by S phase checkpoint functions in Saccharomyces cerevisiae.Myung K et al
173332632007Expression changes of the MAD mitotic checkpoint gene family in renal cell carcinomas characterized by numerical chromosome changes.Pinto M et al
187912702008Overexpression of the mitotic checkpoint genes BUB1 and BUBR1 is associated with genomic complexity in clear cell kidney carcinomas.Pinto M et al
270300092016Functional and Structural Characterization of Bub3·BubR1 Interactions Required for Spindle Assembly Checkpoint Signaling in Human Cells.Prinz F et al
193721382009Enhanced genomic instabilities caused by deregulated microtubule dynamics and chromosome segregation: a perspective from genetic studies in mice.Rao CV et al
113553002001Mutation analysis of hBUB1, hBUBR1 and hBUB3 genes in glioblastomas.Reis RM et al
101982561999Phosphorylation of human MAD1 by the BUB1 kinase in vitro.Seeley TW et al
287672892017Deleterious Germline Mutations in Patients With Apparently Sporadic Pancreatic Adenocarcinoma.Shindo K et al
304133202019Over expression of DNA damage and cell cycle dependent proteins are associated with poor survival in patients with adrenocortical carcinoma.Subramanian C et al
115356162001Checkpoint inhibition of the APC/C in HeLa cells is mediated by a complex of BUBR1, BUB3, CDC20, and MAD2.Sudakin V et al
201012362010Integrative molecular profiling of triple negative breast cancers identifies amplicon drivers and potential therapeutic targets.Turner N et al
172688142007Genetic variation in the major mitotic checkpoint genes does not affect familial breast cancer risk.Vaclavicek A et al
191825302009TAp73alpha binds the kinetochore proteins Bub1 and Bub3 resulting in polyploidy.Vernole P et al
259182252015Splicing function of mitotic regulators links R-loop-mediated DNA damage to tumor cell killing.Wan Y et al
247111382014Genetic variation in the major mitotic checkpoint genes and risk of breast cancer: a multigenic study on cancer susceptibility.Wang P et al
204423142010Expression of oncogenic kinase Bcr-Abl impairs mitotic checkpoint and promotes aberrant divisions and resistance to microtubule-targeting agents.Wolanin K et al
222343452012Bone morphogenetic protein (BMP) signaling regulates mitotic checkpoint protein levels in human breast cancer cells.Yan H et al
155851352004Proteomic analysis of antiproliferative effects by treatment of 5-fluorouracil in cervical cancer cells.Yim EK et al
164284792006Increased expression of mitotic checkpoint genes in breast cancer cells with chromosomal instability.Yuan B et al
237473382013Germline mutations in the spindle assembly checkpoint genes BUB1 and BUB3 are risk factors for colorectal cancer.de Voer RM et al

Other Information

Locus ID:

NCBI: 9184
MIM: 603719
HGNC: 1151
Ensembl: ENSG00000154473


dbSNP: 9184
ClinVar: 9184
TCGA: ENSG00000154473


Gene IDTranscript IDUniprot

Expression (GTEx)



PathwaySourceExternal ID
Cell cycleKEGGko04110
Cell cycleKEGGhsa04110
HTLV-I infectionKEGGko05166
HTLV-I infectionKEGGhsa05166
Signal TransductionREACTOMER-HSA-162582
Signaling by Rho GTPasesREACTOMER-HSA-194315
RHO GTPase EffectorsREACTOMER-HSA-195258
RHO GTPases Activate ForminsREACTOMER-HSA-5663220
Cell CycleREACTOMER-HSA-1640170
Cell Cycle CheckpointsREACTOMER-HSA-69620
Mitotic Spindle CheckpointREACTOMER-HSA-69618
Inhibition of the proteolytic activity of APC/C required for the onset of anaphase by mitotic spindle checkpoint componentsREACTOMER-HSA-141405
Inactivation of APC/C via direct inhibition of the APC/C complexREACTOMER-HSA-141430
Cell Cycle, MitoticREACTOMER-HSA-69278
Mitotic PrometaphaseREACTOMER-HSA-68877
Resolution of Sister Chromatid CohesionREACTOMER-HSA-2500257
Mitotic Metaphase and AnaphaseREACTOMER-HSA-2555396
Mitotic AnaphaseREACTOMER-HSA-68882
Separation of Sister ChromatidsREACTOMER-HSA-2467813
Regulation of mitotic cell cycleREACTOMER-HSA-453276
APC/C-mediated degradation of cell cycle proteinsREACTOMER-HSA-174143
Regulation of APC/C activators between G1/S and early anaphaseREACTOMER-HSA-176408
Activation of APC/C and APC/C:Cdc20 mediated degradation of mitotic proteinsREACTOMER-HSA-176814
APC/C:Cdc20 mediated degradation of mitotic proteinsREACTOMER-HSA-176409
APC:Cdc20 mediated degradation of cell cycle proteins prior to satisfation of the cell cycle checkpointREACTOMER-HSA-179419
Cdc20:Phospho-APC/C mediated degradation of Cyclin AREACTOMER-HSA-174184
APC-Cdc20 mediated degradation of Nek2AREACTOMER-HSA-179409

Protein levels (Protein atlas)

Not detected


Pubmed IDYearTitleCitations
240662272013Bub3 reads phosphorylated MELT repeats to promote spindle assembly checkpoint signaling.84
256614892015Sequential multisite phospho-regulation of KNL1-BUB3 interfaces at mitotic kinetochores.39
207340642010A large-scale candidate gene association study of age at menarche and age at natural menopause.38
181996862008The human spindle assembly checkpoint protein Bub3 is required for the establishment of efficient kinetochore-microtubule attachments.37
237473382013Germline mutations in the spindle assembly checkpoint genes BUB1 and BUB3 are risk factors for colorectal cancer.32
172896652007The DYNLT3 light chain directly links cytoplasmic dynein to a spindle checkpoint protein, Bub3.26
261485132015Dissecting the roles of human BUB1 in the spindle assembly checkpoint.25
153883282004WD repeat-containing mitotic checkpoint proteins act as transcriptional repressors during interphase.19
252465572014Bimodal activation of BubR1 by Bub3 sustains mitotic checkpoint signaling.15
157969612005Allelic loss at 10q26 in osteosarcoma in the region of the BUB3 and FGFR2 genes.13


Jorge Antonio Elias Godoy Carlos ; Joao Agostinho Machado-Neto

BUB3 (BUB3 mitotic checkpoint protein)

Atlas Genet Cytogenet Oncol Haematol. 2019-03-01

Online version: http://atlasgeneticsoncology.org/gene/855/bub3id855ch10q26